1. Field of the Invention
The present invention relates to a gas concentration detection sensor.
2. Description of the Related Art
Gas concentration detection sensors have been known to detect the concentration of a selected gas, for example, NOx or oxygen, included in an object gas, such as emission or exhaust gas from an automobile. In the gas concentration detection sensors, the presence of water generated at an engine start time and adhering to a sensor element or an abrupt increase in flow rate of the object gas flowed against the sensor element may lower the temperature of the sensor element and cause cracking in the sensor element. One proposed measure for preventing the occurrence of cracking provides a protective cover to cover over the sensor element. For example, in a gas sensor disclosed in Patent Document 1, as one example of the protective cover, a protector of a double-layered structure with a vent for introducing the exhaust gas inside the gas sensor is provided around an outer circumference of an edge section of the sensor element.    Patent Document 1: JP 2005-195516 A (FIG. 10)